A genetic screen in Drosophila reveals an unexpected role for the KIP1 ubiquitination-promoting complex in male fertility

Abstract

A unifying feature of polycystin-2 channels is their localization to both primary and motile cilia/flagella. In Drosophila melanogaster, the fly polycystin-2 homologue, Amo, is an ER protein early in sperm development but the protein must ultimately cluster at the flagellar tip in mature sperm to be fully functional. Male flies lacking appropriate Amo localization are sterile due to abnormal sperm motility and failure of sperm storage. We performed a forward genetic screen to identify additional proteins that mediate ciliary trafficking of Amo. Here we report that Drosophila homologues of KPC1 and KPC2, which comprise the mammalian KIP1 ubiquitination-promoting complex (KPC), form a conserved unit that is required for the sperm tail tip localization of Amo. Male flies lacking either KPC1 or KPC2 phenocopy amo mutants and are sterile due to a failure of sperm storage. KPC is a heterodimer composed of KPC1, an E3 ligase, and KPC2 (or UBAC1), an adaptor protein. Like their mammalian counterparts Drosophila KPC1 and KPC2 physically interact and they stabilize one another at the protein level. In flies, KPC2 is monoubiquitinated and phosphorylated and this modified form of the protein is located in mature sperm. Neither KPC1 nor KPC2 directly interact with Amo but they are detected in proximity to Amo at the tip of the sperm flagellum. In summary we have identified a new complex that is involved in male fertility in Drosophila melanogaster. Author summary: In Drosophila, the polycystin-2 homologue, Amo, is found in a restricted area at the tip of the sperm tail where it mediates directed sperm migration and proper sperm storage. The factors involved in Amo trafficking to this distinctive subcellular domain are unknown. We screened a collection of male sterile Drosophila EMS mutants for mislocalization of Amo to gain clues about what proteins that might be involved in this process. Here we report that fly homologues of KPC1 and KPC2 which, form the core of the mammalian KIP1 ubiquitination-promoting complex (KPC) are required for Amo to reach the tip of the sperm tail. In summary, we have uncovered a novel role for the KIP1 ubiquitination-promoting complex in Drosophila sperm and male fertility.

Publication information

Originally published in PLOS Genetics on 2020-12-30. Original DOI: 10.1371/journal.pgen.1009217.

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